The present invention relates to semiconductor circuits and particularly to logic circuits employing threshold functions and employing integrated injection logic devices.
Logic circuits employing threshold functions have been generally known for a long time. Threshold functions generally encompass digital signals which include more levels than the two levels of conventional binary signals. One example of a threshold logic gate is described in U.S. Pat. No. 3,838,393 invented by Tich T. Dao and assigned to the assignee of the present invention. The threshold functions in that patent are generated using emitter-coupled logic (ECL) devices.
Although threshold functions have been well known, they have not been employed widely in the design of semiconductor circuits. One reason that they have not been employed widely is because threshold functions are more complex than simple binary functions. The complexity has apparently discouraged use on a widespread basis whether emitter-coupled logic (ECL), integrated injection logic (I.sup.2 L), or other forms of logic devices are employed.
Injection logic generally includes switching transistors which are controlled by input signals to be either in the conducting (ON) or the non-conducting (OFF) state. In order to enhance the switching characteristics of the switching transistors, semiconductor injection devices (e.g., injection transistor) are utilized to inject carriers into the base regions of the switching transistors. The switching transistors and the injection devices can be integrated into a common structure in order to achieve the general objectives of semiconductor technology.
The general objectives of semiconductor technology are to increase circuit density, increase switching speed, increase reliability, while decreasing cost. It is a general objective of the present invention to provide circuits and semiconductor devices which improve upon these general objectives.